This invention relates to a hermetically sealed package for electro-optical devices, such package having a housing, a lid and a feedthrough for at least one optical fiber.
In known packages for electro-optical devices, e.g. lasers, at least one stripped optical fiber, usually a plurality of fibers, is passed through an opening in the wall of the casing, or housing, of the package and is connected to the device inside. The casing as well as the fiber feedthrough must be sealed to protect the device against environmental hazards e.g. humidity. Since the sealing is usually done with a solder that has a coefficient of thermal expansion (CTE) much greater than that of glass of the fiber, problems arise with significant temperature fluctuations over time as the seal between the fibers and the casing may deteriorate. The problem may still arise even if the fibers are metallized with a solderable metal coating before assembly with the package.
In WO 98/01783, it is proposed to place a number of precoated optical fibers and a solder perform between the sealing surface of the lid and the sealing surface of the housing, and then seal the assembly, i.e. the lid and the fibers in the array, at the same time. This method eliminates ferrules and feedthrough holes in the wall of the apply heat and pressure so as to press the fibers into the solder and seal the assembly at package and appears to work satisfactorily provided that no significant temperature changes are encountered over time.
It is still desirable to provide a hermetically sealed package and a method of sealing the package that would offer a relatively high resistance to temperature changes, or in other words, a compensation of CTE mismatching due to different materials used in the package assembly.
According to one aspect of the invention, there is provided a hermetically sealed package comprising a first casing portion and a second casing portion that functions as a lid. The package has a split feedthrough associated with either the first casing portion, the second portion or both. The feedthrough is composed of two separable parts that when assembled, define a gap therebetween for placing one or more optical fibers extending between the inside and the outside of the package. Further, the package comprises fasteners for securing the first and second feedthrough parts together. The first and second casing portions as well as the fibers in the gap are sealed with solder in one operation.
The feedthrough may comprise, on one or both of its parts, grooves for accommodating one or more optical fibers. The size of the grooves is larger than the diameter of the fibers to allow a solder to flow around the fibers for effective sealing.
In one embodiment of the invention, a first casing portion is associated with a first feedthrough part and the second casing portion is associated with a second, matching feedthrough part. Alternatively, only one feedthrough part may be associated with a first (or second) casing portion while the second feedthrough part forms a separate element that can be assembled with the first feedthrough part with the fasteners.
Preferably, the solder material is selected to exhibit good wettability of glass and relatively high compressive strength. The CTE of the solder is also an important consideration.
In another aspect of the invention, there is provided a method of making a hermetically sealed package which package comprises a first casing portion, a second matching casing portion and a feedthrough for at least one stripped optical fiber, the method comprising
placing the optical fiber or fibers in the feedthrough,
assembling the first and second casing portions and fastening them together to form a feedthrough gap therebetween, the fiber or fibers being disposed in the gap,
feeding a molten solder material into the gap, and
sealing the feedthrough and the first and the second casing portion,
wherein the fastening step is effected before the solder feeding step and the sealing step.
Preferably, the solder material is a material that expands upon solidification and is capable of sealing the first and second casing portion.
Preferably, at least the area of the package to be sealed is heated at or about the time that the gap is filled with the solder material.